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Date: Wed, 17 Feb 2016 15:00:52 -0800
From: Kees Cook <>
To: David Brown <>
Cc: Russell King <>, 
	"" <>, 
	"" <>, Ingo Molnar <>, 
	Andy Lutomirski <>, "H. Peter Anvin" <>, 
	Michael Ellerman <>, Mathias Krause <>, 
	Thomas Gleixner <>, "" <>, Arnd Bergmann <>, 
	PaX Team <>, Emese Revfy <>, 
	LKML <>, linux-arch <>
Subject: Re: [PATCH] ARM: vdso: Mark vDSO code as read-only

On Tue, Feb 16, 2016 at 9:20 PM, David Brown <> wrote:
> On Tue, Feb 16, 2016 at 01:52:33PM -0800, Kees Cook wrote:
>> On Tue, Feb 16, 2016 at 1:36 PM, David Brown <>
>> wrote:
>>> Although the arm vDSO is cleanly separated by code/data with the code
>>> being read-only in userspace mappings, the code page is still writable
>>> from the kernel.  There have been exploits (such as
>>> that take advantage of this on x86 to go
>>> from a bad kernel write to full root.
>>> Prevent this specific exploit on arm by putting the vDSO code page in
>>> post-init read-only memory as well.
>> Is the vdso dynamically built at init time like on x86, or can this
>> just use .rodata directly?
> On ARM, it is patched during init.  Arm64's is just plain read-only.

Okay, great. I've added this to my postinit-readonly series (which I
just refreshed and sent out again...)


Kees Cook
Chrome OS & Brillo Security

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